This application is also related to concurrently filed non-provisional application by G. J. Foschini, et al. entitled High-Speed Data Services Using Multiple Transmit Antennas, which non-provisional application is assigned to the assignee of the present invention.
The present invention relates to high-speed wireless communication systems and methods. More particularly, the present invention relates to such communications systems and methods offering mobile multiple access for voice and data communications users. Still more particularly, the present invention relates to such wireless communications systems and methods employing multiple transmit and receive antenna structures.
Mobile wireless voice communications systems and services are presently in widespread use. Provision of high-speed wireless packet data services for web browsing, multimedia delivery and other applications is an important goal for evolving wireless systems and services, especially those based on code division multiple access (CDMA) systems.
While proposals have been made for providing high-speed data using schemes such as multicode and variable spreading gain, these do not address limitations based on insufficient cell capacity; these techniques merely involve trading voice capacity for data capacity. High-speed data systems for simultaneously supporting multiple data users requires a significant increase in spectral efficiency-measured in bits/chip per sector or equivalently, bits per second per Hertz per sector. See generally, K. S. Gilhousen. I. M. Jacobs, R Padovani, A. J. Viterbi, L. A Weaver Jr., C. E. Wheatley III. xe2x80x9cOn the Capacity of a Cellular CDMA System,xe2x80x9d IEEE Trans. on Vehicular Technology, 40, No.2: 303-312, May 1991.
In G. J. Foschini, xe2x80x9cLayered Space-Time Architecture for Wireless Communication in a Fading Environment When using Multi-Element Antennas,xe2x80x9d Bell Labs Tech. J., Autumn 1996, pp. 41-59, a communication technique is described for achieving very high data rates in a wireless system using multiple transmit antennas, multiple receive antennas, and advanced signal processing at the receiver. High data rates in such systems can be attributed to many factors, including the effects of a rich scattering environment that causes a signal from a single transmitter to appear highly uncorrelated at each of the receive antennas, and the benefits of advanced signal processing at the receiver for separating the signals from multiple transmit antennas in a near-optimum fashion using multiple receive antennas. The context of the last-cited Foschini paper is that of narrowband channels and point-to-point communications, rather than systems for high-speed data services in a cellular CDMA system.
Limitations of the prior art are overcome and a technical advance is made in accordance with the present invention, illustrative embodiments of which are described below. In one aspect, the present invention provides high-speed data systems and methods for simultaneously supporting multiple data users. Moreover, present inventive embodiments provide flexible mixed-traffic services that simultaneously provide different data rates for each of a plurality of users, including high rate data and voice users.
In illustrative embodiments described below, a physical layer, CDMA architecture is disclosed for providing such high-speed systems and related services. Embodiments of the present invention are compatible with current and third generation CDMA systems (such as the US CDMA2000 and European/Japanese Wideband CDMA systems), and achieve spectral efficiencies that are in some cases an order of magnitude or more higher than those of current systems.
As in point-to-point narrowband systems described, e.g., in the above-cited Foschini paper, embodiments of the present invention advantageously employ multiple antennas at the transmitter and receiver. However, unlike such prior systems, presently disclosed embodiments include the use of code spreading to realize multiple access systems simultaneously supporting multiple users. Inventive architectures and configurations are described to meet the demand for high-speed data services to mobile users.
In accordance with another aspect of the present invention, some illustrative receiver embodiments advantageously employ a decorrelating detector, while other illustrative embodiments feature a decorrelating decision-feedback detector.
In providing backward compatibility for traditional services, voice users are typically assumed to use conventional single antenna receivers, and their signals are transmitted from the base station using a single antenna. In contrast, mobile data users can employ multiple antennas and advanced signal processing, and signals are received from multiple base station antennas. Present inventive principles are illustratively applied to transmission and detection of high data rate signals; transmission and detection of low-rate (e.g., voice) signals is unchanged and can operate simultaneously with systems and methods employing teachings of the present invention.
In typical operation, each of a plurality of high-speed data streams directed to respective data users is demultiplexed into multiple lower rate substreams. In general, the rates of both the high-speed data streams and the lower rate substreams can be different. However, for illustrating the principles of this invention, it proves convenient to assume that the high data rate streams are the same for all users and that these streams are each demultiplexed into G greater than 1 lower rate substreams. Each of these substreams illustratively has the same rate as a conventional voice data stream. These substreams are modulated by a CDMA spreading code and transmitted from M antennas at a base station. The receiver employs P antennas and multi-user detection to demodulate the G data substreams associated with a user.
Performance measures for each of a variety of different transmission and receiver techniques are illustratively derived in terms of spectral efficiency measured in bits per chip per sector. In particular, it proves advantageous to determine the number of users that can be supported in a sector at a given data rate, error rate and outage rate. It proves useful to perform analyses of spectral efficiencies of CDMA systems using simulations of multiple antennas and multi-user detectors in combination with simulations of link level bit error rate performance and system level signal-to-interference ratios.
Novel techniques are provided for calculating system level capacities and spectral efficiencies (measured in bits per second per Hertz per sector) by incorporating link level results with system level outage simulations. System spectral efficiency is then determined as a function of various parameters (e.g., number of transmit antennas. transmit diversity order, random or orthogonal code transmission, same or different code transmission, number of receive antennas, and type of receiver). Thus, system design and configuration tradeoffs are readily made based on such performance determinations. A number of selection considerations and design examples are presented below.
Using presently disclosed inventive techniques, illustrative systems support 64 users per 120-degree sector, each at 76.8 Kbps in a 1.25 MHz band, with a spectral efficiency equal to 4 bps/Hz per sectorxe2x80x94an order if magnitude greater than that of a conventional (single-antenna) voice CDMA system. Other illustrative embodiments permit design of systems supporting even higher data rate users and a variety of mixed rate traffic. Thus, for example, other illustrative embodiments of the present invention g support seven high-speed data users per sector, each operating at 384 Kbps, simultaneously with 8 voice users, each at 9.6 Kbps. Such results are illustratively realized in systems employing four transmit antennas at the base station and laptop-sized mobile receiver devices, each using twelve receive antennas and an illustrative multi-user detection algorithm.